Protection of double end exposed systems

ABSTRACT

The present invention discloses systems and methods for protecting electronic devices (switching and non-switching) such as micro electro-mechanical system (MEMS) devices and solid state relays due to lightning exposure or electrical power surges in double end exposed systems. Over voltage suppressors and over current detectors are used to limit the exposure of high voltages and currents to the MEMS and solid-state relay devices in double end exposed systems.

FIELD OF THE INVENTION

[0001] The present invention relates to the field of telecommunicationnetworks. The present invention is also directed to systems and methodsfor protecting devices such as micro electro-mechanical system (MEMS)and electronic relay devices in telecommunication systems. Moreparticularly, the present invention is directed to systems and methodsfor protecting cross connect units that are implemented with MEMS orsolid state relay devices in double end exposed systems.

BACKGROUND OF THE INVENTION

[0002] Micro electro-mechanical system (MEMS) and solid-state relay(SSR) devices are used as alternatives for conventionalelectromechanical switching devices. As is well known, the conventionaldevices possess some highly desirable characteristics such as lowcontact resistance, high voltage breakdown, and relatively high currenthandling capability, which characteristics make them ideal for use intelecommunication systems. However, such conventional devices are notwell suited for miniaturization or integration.

[0003] MEMS and SSR devices can perform the standard functions ofconventional relays and are well suited for miniaturization andintegration. MEMS devices are basically miniaturized electro-mechanicaldevices that are fabricated using techniques similar to those used forsemiconductor integrated circuits and are well suited for low cost andhigh volume production. MEMS device applications have been used aspressure sensors, chemical sensors, light reflectors, switches, andrelays. MEMS devices are low cost devices due to the use ofmicroelectronic fabrication techniques, and new functionality may alsobe provided because they are much smaller than conventional devices.

[0004] However, MEMS and SSR devices have several major shortcomings anddisadvantages. The most notable disadvantage is that these devices arerelatively fragile in current carrying and voltage breakdowncapabilities. For example, because MEMS and SSR devices are relativelyfragile, lightning or AC power surges can completely destroy them.Lightning is characterized by very high voltage and current of veryshort duration pulses, i.e., less than 1.0 ms, whereas AC power surgesor faults are characterized by very high voltage and current ofrelatively long duration pulses, i.e., seconds. As a result, systemshaving MEMS or SSR devices therein can become disabled and/or destroyedquite easily.

[0005] There are currently different systems and methods for protectingMEMS and SSR devices from lightning and/or AC power surges. But, none ofthese conventional systems and methods is directed towards protectingMEMS and SSR devices that are implemented within units such as crossconnect systems, e.g., the “CX 100 CrossConnect System” from TurnstoneSystems, Inc. The CX100 Copper CrossConnect System is a platform thatautomates the physical layer infrastructure in the central office,enabling ILECs (incumbent local exchange carrier) and CLECs (competitivelocal exchange carrier) to remotely control, test, and manage a copperloop. Additional information regarding Turnstone System's CX100 CopperCrossConnect System can be found at its web site turnstone.com. It isalso noted that other systems and units providing similarfunctionalities as the CX100 Copper CrossConnect System can beimplemented in the present invention.

[0006] In cross connect applications, the system can be configured ineither a “single end exposed system” or a “double end exposed system.”For a more comprehensive understanding of the above-identified systemsand the present invention, the following terms have been defined asfollows:

[0007] (1) a “pass-through system” is a system that provides connectionbetween an input port and an output port through a pair of metallicconductors characterized by relatively low ohmic resistance;

[0008] (2) an “ingress port” is a signal entering an equipment; and

[0009] (3) an “egress port” is a signal exiting an equipment.

[0010]FIG. 1 illustrates a simplified block diagram of a conventionalsingle end exposed system. The single end exposed system is a systemwhere one port, such as the ingress port 2, is connected to an “outsideplant” equipment, and the other port, such as the egress port 4, isconnected to an “in-building” equipment or termination unit, such as aCentral Office (CO) equipment. In this diagram, the ingress port 2 isidentified by terminals T1 and R1, while the egress port 4 is identifiedby terminals T2 and R2.

[0011] In greater detail, the ingress port 2 provides connection to the“outside plant”, an over voltage protector (“OVP”) 6, and an EquipmentUnder Protection (“EUP”) 8. The egress port 4 provides connection to theEUP 8 and the termination within the “in-building” equipment. The EUP 8represents a metallic cross connect unit or the like and is implementedwith MEMS or SSR devices. As discussed above, over voltage and/or overcurrent can easily damage the MEMS or SSR devices within the EUP 8.Typically, the OVP 6 protects the MEMS or SSR devices from over voltageconditions. An over current protector (“OCP”) (not shown) can also beused to protect the MEMS or SSR devices from over current conditions.The OCP function is usually performed by the termination unit with acurrent limiter, such as a resistor of appropriate value.

[0012] The OVP 6 is implemented only in between the ingress port 2 andthe EUP 8. Since the connection between the egress port 4 and the EUP 8is generally not exposed to voltage surges, another OVP is not requiredin between the egress port 4 and the EUP 8. A co-pending U.S. patentapplication Ser. No. 09/677,483, commonly owned by the assignee ofrecord, discloses improved methods and systems for protecting MEMS andSSR devices in the single end exposed system.

[0013]FIG. 2 illustrates a simplified block diagram of a conventionaldouble end exposed system. The double end exposed system is a systemwhere both ports, ingress 2 and egress 4, are connected to the “outsideplant” equipment. The double end exposed system includes over voltageprotectors, OVP-I 12 and OVP-E 14, near the ingress and egress ports,respectively, which ports can be exposed to lightning and AC powersurges. In other words, lightning and AC power surges can enter fromeither side of the EUP 8 and thus, both sides of the EUP 8 need to beprotected.

[0014]FIG. 3 illustrates a more detailed diagram of the conventionaldouble end exposed system of FIG. 2. In FIG. 3, the term “OP” replacesthe term “OVP” of FIG. 2 for ease of explanation. As illustrated, theingress port represented by terminals T1 and R1 can be connected to theV_(s) and Rs, where V_(s) represents a surge source generator and Rsrepresents the corresponding source resistance. Likewise, the egressport represented by terminals T2 and R2 can be connected to atermination equipment 20. The over voltage protectors are represented byOP1 and OP2 in proximity to the ingress port, and by OP3 and OP4 inproximity to the egress port. In addition, the resistors RC1 and RC2represent the finite contact resistance associated with the MEMS device22. The EUP 8 is represented by the MEMS device 22 for ease ofexplanation.

[0015] The over voltage protectors or OPs are characterized by manyparameters, but the key parameters for the purposes of understanding thepresent invention is the break-over or switching voltage represented byV_(bo) and the device on-state voltage represented by V_(on). Other keyparameters include the current handling capability, switching speed, andthe standoff voltage V_(drm). The standoff voltage V_(drm) is defined asthe maximum voltage across the device without having to turn the device“on,” and the break-over voltage V_(bo) is defined as the minimumvoltage across the device to turn it on (i.e., device changing from“off” to “on” state). The selection of this voltage is dictated by themaximum voltage that the MEMS device 22 can withstand without failure.The on-state voltage V_(on) is the voltage drop across the device whenit is turned on and is generally in the range of 1.0 to 3.0 volts,depending on the amount of current flowing through the device.

[0016] For typical CO application, the required standoff voltage V_(drm)is approximately 200V minimum. The break-over voltage V_(bo) is selectedto be approximately 300V maximum, which can “fire”(break-over/switchover) to turn itself on. In fact, the device can turnitself on anywhere between 220V to 300V. This wide break-over voltageV_(bo) range is dictated by technology and manufacturing tolerances.

[0017] A closer view of the diagram of FIG. 3 reveals that the circuitis symmetrical with respect to the ground G. In an effort to simplifythe explanation of the problem associated with this system, FIG. 4illustrates a section (upper half) of the conventional double endexposed system of FIG. 3. FIG. 4 illustrates the terminals T1 and T2 inparallel to the ground G. As illustrated, the surge source V_(s) ispositioned in between the terminal T1 and the ground G through itssource resistance Rs. The resistor RC1 is the equivalent MEMS contactresistance, and the over voltage protectors OP1 and OP3 are assumed toinclude the same characteristics, nominally. Due to inherent toleranceassociated with the break-over voltage V_(bo) of both the over voltageprotectors OP1 and OP3, the following scenarios can exist.

[0018] First, when the surge source V_(s) is less than the break-overvoltage V_(bo) of either of the over voltage protectors OP1 or OP3, nocurrents are flowing within the circuit. In other words, this means thatcurrents i0=i1=i3=0, which means that there are no currents flowing.Accordingly, the MEMS device 22 is protected.

[0019] Second, when the break-over voltage V_(bo) of the over voltageprotector OP1 is less than the break-over voltage V_(bo) of the overvoltage protector OP3, the over voltage protector OP1 will turn on whensurge source V_(s) reaches the break-over voltage V_(bo) of the overvoltage protector OP1. Then, the surge current i0 will naturally flowthrough the over voltage protector OP1. This current will be essentiallyequal to all surge currents (i.e., i0=i1). The voltage across the overvoltage protector OP1, as represented by V₁, is V_(on) in the range of1.0 to 3.0 volts. In this scenario, there is no current flowing throughthe over voltage protector OP3 (i.e., i3=0) and, hence the MEMS device22 is protected from surge currents.

[0020] Third, when the break-over voltage V_(bo) of the over voltageprotector OP1 is greater than the break-over voltage V_(bo) of the overvoltage protector OP3, the over voltage protector OP3 will turn on whenthe surge source V_(s) reaches the break-over voltage V_(bo) of the overvoltage protector OP3. The voltage across the over voltage protectorOP3, as represented by voltage V₃, is V_(on) in the range of 1.0 to 3.0volts. The over voltage protector OP1 is kept in the off-state modeuntil the surge current flowing through the resistor RC1 and the overvoltage protector OP3 produces voltage large enough to reach thebreak-over voltage V_(bo) of the over voltage protector OP1. In otherwords, the over voltage protector OP1 is kept in the off-state mode, andthere is no current flowing through it (i.e., i1=0). In the meantime,the current flowing through the resistor RC1 and the over voltageprotector OP3 is the same as the surge current (i.e., i3=i0), and suchcurrent will likely damage or destroy the MEMS device 22.

[0021] Fourth, when the break-over voltage V_(bo) of the over voltageprotectors OP1 and OP3 are exactly the same, which is a rare case, boththe over voltage protectors OP1 and OP2 will turn on and the surgecurrent will flow through both protectors. The amount of current flowingthrough the two protectors will be split between the two, the amountdepending on the exact impedance of the circuit. Such current throughthe resistor RC1 will likely damage or destroy the MEMS device 22.

[0022] As detailed above, the conventional systems and methods forprotecting MEMS and SSR devices in double end exposed systems are foundto be inadequate and unworkable. Accordingly, there is a need for morereliable and efficient systems and methods for protecting MEMS and SSRdevices in double end exposed systems due to lightning exposure orelectrical power surges.

SUMMARY OF THE INVENTION

[0023] In view of the above-described problems of the prior art, it isan object of the present invention to provide systems and methods forprotecting MEMS and electronic relay devices due to lightning exposureor electrical power surges in double end exposed systems.

[0024] It is yet another object of the present invention to providesystems and methods limiting exposure to high voltages and currents tothe MEMS and solid state relay devices in double end exposed systems.

[0025] It is a further object of the present invention to providesystems and methods for sensing a high current condition and therebyenergizing an over voltage suppressor to protect the MEMS and solidstate relay devices in double end exposed systems.

[0026] It is another object of the present invention to provide systemsand methods to protect metallic cross-connect systems implemented withMEMS and solid state relay devices in double end exposed systems.

[0027] These and other objects of the present invention are obtained byproviding over voltage suppressors and over current detectors in systemshaving MEMS or SSR devices. The over voltage suppressors are used toprotect against voltage pulses such as lightning or power surgeexposure. Similarly, the over current detectors are used to protectagainst current pulses. The present invention can be implemented toprotect any number of MEMS or SSR devices used in connection with doubleend exposed systems.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] These and other objects and advantages of the present inventionwill become apparent and more readily appreciated from the followingdetailed description of the presently preferred exemplary embodiments ofthe invention taken in conjunction with the accompanying drawings, ofwhich:

[0029]FIG. 1 illustrates a simplified block diagram of a conventionalsingle end exposed system;

[0030]FIG. 2 illustrates a simplified block diagram of a conventionaldouble end exposed system;

[0031]FIG. 3 illustrates a more detailed diagram of the conventionaldouble end exposed system of FIG. 2;

[0032]FIG. 4 illustrates a section of the conventional double endexposed system of FIG. 3;

[0033]FIGS. 5A and 5B illustrate simplified block diagrams in accordancewith the preferred embodiments of the present invention;

[0034]FIG. 6 illustrates a more detailed diagram of the double endexposed system of FIG. 5A;

[0035]FIG. 7 illustrates an upper half section of the circuitry shown inFIG. 6;

[0036]FIG. 8 illustrates a detailed circuit diagram of an over voltagesuppressor and an over current detector in accordance with oneembodiment of the present invention; and

[0037]FIGS. 9A and 9B illustrate detailed circuit diagrams of an overvoltage suppressor and an over current detector in accordance withanother embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] The present invention will now be described in greater detail,which will serve to further the understanding of the preferredembodiments of the present invention. As described elsewhere herein,various refinements and substitutions of the various embodiments arepossible based on the principles and teachings herein.

[0039] The preferred embodiments of the present invention will bedescribed with reference to FIGS. 5-9, wherein like components aredesignated by like reference numerals throughout the various figures.Further, specific parameters such as system architecture, circuitlayouts, electronic components, component values, and the like areprovided herein, and are intended to be explanatory rather thanlimiting.

[0040] The present invention is directed to systems and methods forprotecting devices (switching and non-switching) such as MEMS andelectronic relay devices in double end exposed systems. In other words,the present invention is directed to systems and methods for protectingMEMS and electronic relay devices due to lightning exposure orelectrical power surges, and in particular, the use of these type ofdevices in telecommunication equipment such as metallic cross connectsystems.

[0041] The present invention discloses systems and methods forprotecting devices have MEMS or SSR devices such as a metallic crossconnect system in applications where both the ingress and egress portsare connected to an equipment residing in the outside plant, therebyexposing the device to potential damages caused by lightning and ACpower faults. According to the present invention, the MEMS device isprotected by insuring that the voltage and current exposed to the deviceis less than or equal to specification limits of the MEMS device. TheMEMS device is protected regardless of any of the four scenariosdescribed in the Background Section of this Specification. This isaccomplished by introducing over voltage/over current protectors havingover voltage suppressors and over current detectors.

[0042] The over voltage suppressors limit/clamp the voltage that isexposed to the MEMS device, and sense resistors are used to sense a highcurrent such that the over current protectors block the high currentfrom damaging or destroying the MEMS device. The over voltagesuppressors are also used to protect against voltage pulses such aslightning or power surge exposure. Similarly, the over currentprotectors are used to protect against current pulses.

[0043]FIGS. 5A and 5B illustrate simplified block diagrams in accordancewith the preferred embodiments of the present invention. Circuitrydescribed and illustrated in reference to FIGS. 5A and 5B areimplemented in double end exposed systems, and operate similarly. Themain difference between the circuitry of FIGS. 5A and 5B is that in FIG.5A the ground G and the M1 and M2 connections of the OVCP-1 and OVCP-2(defined below) is positioned away from the MEMS device 22, and in FIG.5B the ground G and the M1 and M2 connections of the OVCP-1 and OVCP-2is positioned towards the MEMS device 22. As such, the followingdescription will focus only on the circuitry illustrated in FIG. 5A. Thefollowing terms are defined as follows for a more complete understandingof the present invention:

[0044] Ingress port is identified by terminals T1 and R1;

[0045] Egress port is identified by terminals T2 and R2;

[0046] OVCP-1 is the over voltage/current protector for the ingressport;

[0047] OVCP-2 is the over voltage/current protector for the egress port;

[0048] OVS is defined as the over voltage suppressor;

[0049] OCD is defined as the over current detector;

[0050] R1 and R2 are sense resistors for the ingress port;

[0051] R3 and R4 are sense resistors for the egress port;

[0052] RC1 and RC2 are equivalent resistance of the MEMS device; and

[0053] the OVCP-1 and OVCP-2 should have similar characteristics.

[0054] In this diagram, a cross connect or similar unit having MEMS orSSR array (collectively known as “MEMS device 22”) therein is positionedin between the OVCP-1 102 and OVCP-2 104. The term “MEMS device 22” usedherein can be any electronic, electro-mechanical, etc. device such asMEMS, SSR, and conventional mechanical relay that has switchingcapabilities.

[0055] In greater detail, the MEMS device 22 includes n number ofcontact pairs, where n represents any number. Each contact isrepresented by the “x” symbol in the figures, and each contact pair (onefrom the tip wire and one from the ring wire) represents a controllableentity. Accordingly, the MEMS device 22 as illustrated in FIGS. 5A and5B includes four controllable entities. Although only four controllableentities are illustrated in the figures for simplicity and ease ofexplanation, the number of controllable entities in the MEMS device 22can be more or less than four, depending on the particular systemarchitecture. The current rating of these contacts are relatively low,and the voltage breakdown across open contacts, and between contacts ofdifferent pairs, and between contacts and the body of the MEMS device22, are also relatively low. Therefore, any current and voltage thatexceeds a rated value will likely damage the MEMS device 22.

[0056] The MEMS device 22 is also connected to a tip (T) and ring (R)pair. The tip and ring pair is used to deliver both voice and/or dataservices to customers. The MEMS device 22 is typically exposed to acertain level of voltage and current that is tolerable. However, thesedevices can be easily damaged or destroyed when they are exposed to highvoltages or currents. The present invention is intended to protect theMEMS device 22 from damage, and, in particular when implemented indouble end exposed systems.

[0057]FIG. 6 illustrates a more detailed diagram of the double endexposed system of FIG. 5A. In particular, FIG. 6 illustrates a moredetail diagram of the OVCP-1 102 and OVCP-2 104. Each OVCP consists oftwo identical circuits with one protecting the tip path and the otherthe ring path, respectively. Furthermore, the overall circuit topologyis symmetrical with respect to ground G.

[0058] With reference to OVCP-1 102, it includes an OVS coupled to anOCD, which itself is coupled to a sense resistor R1. The sense resistorR1 is further coupled to the OVS and the tip wire. As described above,the sense resistor R1 senses high currents such that the OCD willgenerate a signal to trigger OVS so that it can be activated to protectthe MEMS device 22. When a lightning exposure or AC power surge occurs,the sense resistor R1 senses the current across it. The OCD compares theresulting voltage with a predefined value and if a threshold isexceeded, a signal is generated to trigger the OVS.

[0059] The OVS is used to limit the maximum voltage limit that the MEMSor SSR devices can be exposed. For example, when the voltage increasesbecause of lightning exposure (i.e., 1000 V) or AC power surge, the OVSis used to clamp/limit the voltage to some predetermined maximum valuethat the MEMS device 22 can handle. The range of this value is betweenthe maximum operating voltage under normal condition (lower limit) andthe maximum tolerable voltage (upper limit) of the MEMS device 22. Sincethe lightning is a very fast event (microsecond), the OVS needs toclamp/limit the voltage and is designed to respond in nanoseconds. TheOCD is also a fast detecting device capable of responding to lightninginduced currents.

[0060]FIG. 7 illustrates an upper half section of the circuitry shown inFIG. 6. Detailed operation description will be provided with respect toFIG. 7, which is also applicable to the ring path. The OVCP for theingress port is the OVCP-1 and for the egress port is the OVCP-2. TheOVS and OCD in the OVCP-1 are represented as OVS1 112 and OCD1 122,respectively. Similarly, the OVS and OCD in the OVCP-2 are representedas OVS2 114 and OCD2 124. The sense resistors R1 and R2 are associatedwith the OVCP-1 and OVCP-2, respectively.

[0061] The OVS limit/clamp the voltage that is exposed to the MEMSdevice 22. The voltage characteristics and operation behavior for theOVP as previously discussed in the context of FIG. 4 are also applicableto the OVS. The parameters V_(drm), V_(bo), and V_(on) are alsoapplicable to the OVS as described earlier. However, the OVS differsfrom the OVP in that that the OVS can be turned-on by an externaltriggering signal (i.e., tg1 for OVCP-1 and tg2 for OVCP-2).

[0062] The OCD senses the current flowing in the sense resistor R. Ifthe current exceeds a threshold value, a triggering signal tg isgenerated and is used to turn on the OVS. When the OVS is turned on,current will be diverted from the sense resistor to flow thorough theOVS, and hence protect devices, such as the MEMS device 22, that areconnected in series with the sense resistor R. The OCD current detectionthreshold value is chosen to protect the MEMS device (RC1) 22 from beingdamaged or destroyed.

[0063] An overall system operation behavior will now be described withreference to FIG. 7. A surge source, as represented by V_(s) and Rs, isconnected to the ingress port at terminals T1 and ground G. Anequivalent load, Rt, is connected to the egress port at terminals T2 andground G. The resistor RC1 represents the MEMS device 22 that requiresprotection. The generator current can flow in the path established bycurrent path i1 and/or i2. Ideally, the surge current should flow in apath defined by current i2 to protect the resistor RC1.

[0064] When the surge generator is applied to terminals T1 and ground G,the circuit behavior is dependent on the characteristics of OVCP-1 andOVCP-2. The scenarios as discussed earlier are repeated herein asfollows.

[0065] First, when the surge source V_(s) is less than the break-overvoltage V_(bo) of either the OVS1 112 or OVS2 114, both OVS1 112 andOVS2 114 remain in the off-state modes, and there will be no currentflowing out of ground G of OVCP-1 and OVCP-2. The surge current can thenflow through resistors R1, RC1, R2, and Rt, and as indicated by currenti1. The magnitude of current i1 is dependent on the value of Rt. If thevalue of current i1 reaches the prescribed threshold of OCD1 122, atriggering signal tg1 is generated, and OVS1 112 is turned on. Then, allsurge currents are diverted away from the MEMS device 22. The voltageacross OVS1 112 as represented by V1 is V_(on) in the range of 1.0-3.0volts. Nearly all surge current will now flow as current i2, andaccordingly, the MEMS device 22 will be protected. This mechanismprotects the MEMS device 22 from over current damage regardless of thevoltage.

[0066] Second, when the break-over voltage V_(bo) of OVS1 112 is lessthan the break-over voltage V_(bo) of the OVS2 114, the OVS1 112 willturn on when V_(s) reaches its V_(bo). The surge current will flow ascurrent i2. The voltage V1 across OVS1 112 is V_(on) 1, in the range of1.0-3.0 volts, which indicates the on-state voltage. The current i1through the resistor RC1 is near zero or relatively small depending onthe value of the resistor Rt. Again, the MEMS device 22 will beprotected, and this method insures that the voltage and current of theMEMS device 22 are not exceeded.

[0067] Third, when the break-over voltage V_(bo) of the OPS1 112 isgreater than the break-over voltage V_(bo) of OPS2 114, this will resultin the undesirable scenario causing OVS2 114 to turn on before OVS1 112is turned on. As V_(s) reaches the V_(bo) of OVS2 114 before that ofOVS1 112, OVS2 114 will turn on. The surge current will flow as currenti1. The voltage V2 across OVS2 114 is V_(on), and the OVS2 114 willcarry nearly all the surge currents. The surge currents as current i1will flow through the resistor R1, and when it reaches the threshold ofOCD1 122, the triggering signal tg1 is generated. In turn, this signaltriggers OVS1 112 to the on-state mode and diverts all or nearly all ofthe surge away from the resistor RC1, thereby preventing damage to theMEMS device 22. The surge currents will then flow through OVS1 112. Thismethod protects the MEMS device 122 from over-voltage and over-currentdamages.

[0068] Fourth, when the break-over voltage V_(bo) of the OVS1 112 andOVS2 114 are exactly the same, it is possible for both OVS1 112 and OVS2114 to turn on simultaneously. In this case, the surge is flowed ascurrents i1 and i2. Due to finite resistance value attributed to the sumof resistors R1, RC1, and R2, combined with the on-state behavior of theOVS1 112 and OVS2 114, nearly all surge currents will flow through OVS1112, and the current flowing through RC1 will be greatly reduced. Again,the MEMS device 122 is protected.

[0069] Due to the symmetrical nature of the circuit topology, theingress and egress ports can be interchanged and the descriptionprovided above is equally applicable. Furthermore, the direction of thecurrent flow as depicted by currents i1 and i2, and the voltagepolarities as exemplified by V1 and V2, shown in FIG. 7, can bereversed, and the circuit operation as described herein are valid.

[0070] The circuit topology for the OVCP consists of two circuitelements with each having blocks designated as OVS and OCD,respectively. The OVS is a solid state device having a designedin-voltage breakdown threshold so that when it is exceeded, the OVS willturn itself on. In addition, the OVS can also be induced to turn on witha trigger signal. These two features combine to have very similarcharacteristics of a TRIAC. A TRIAC is a particular configurationbelonging to the TYRISTOR family of solid state devices, which have beenavailable as industry standard products.

[0071]FIG. 8 illustrates a detailed circuit diagram of an over voltagesuppressor and an over current detector in accordance with oneembodiment of the present invention. The OVS is similar to a TRIAC, andan OCD is implemented with standard operational amplifier andcomparator. In greater detail, the OCD consists of amplifier A1connected across the resistor R1. The amplifier A1 is also connected toa comparator C1, which output is coupled to the OVS. The comparator C1compares output of the amplifier A1 to a reference voltage, which isselected to be proportional to the over current threshold.

[0072]FIGS. 9A and 9B illustrate detailed circuit diagrams of an overvoltage suppressor and an over current detector in accordance withanother embodiment of the present invention. FIGS. 9A and 9B illustratean implementation combining the OVS and OCD functions into oneintegrated design. FIG. 9A illustrates a Tyristor structure and FIG. 9Bis the equivalent circuit diagram. The OVS consists of zener diode Z andtransistors N1 and N2. The zener diode Z defines the V_(bo).

[0073] The OCD consists of a sense resistor R1, and the PN junction oftransistor N1. The OCD threshold is defined by the combination ofbase-to-emitter voltage drop (V_(be)) of transistor N1 and the value ofresistor R1. The above described components with reference to FIGS. 8,9A and 9B are well known components.

[0074] In the previous descriptions, numerous specific details are setforth such as system architecture, circuit layouts, electroniccomponents, component values, etc. to provide a thorough understandingof the present invention. However, as one having ordinary skill in theart would recognize, the present invention can be practiced withoutresorting to the details specifically set forth.

[0075] Although only the above embodiments have been described in detailabove, those skilled in the art will readily appreciate that manymodifications of the exemplary embodiments are possible withoutmaterially departing from the novel teachings and advantages of thisinvention.

I claim:
 1. A method for protecting a device against damage resultingfrom an electrical power fault in a double end exposed system, whereinthe device is positioned in a copper loop in a telecommunicationnetwork, the method comprising: detecting a current in the copper loop;comparing the sensed current with a threshold current associated withthe device; diverting the current flow from the device to an overvoltage suppressor if the value of the sensed current is greater thanthe value of the threshold current; and limiting an electrical powerfault voltage that is exposed to the device using the over voltagesuppressor.
 2. A method according to claim 1, wherein sensing thecurrent comprises sensing the current across a resistor coupled to thesubscriber loop.
 3. A method according to claim 1, wherein comparing thesensed current with the threshold current comprises using an overcurrent detector coupled to the subscriber loop.
 4. A method accordingto claim 3, wherein the over current protector comprises a comparatorand an amplifier.
 5. A method according to claim 4, wherein an output ofthe amplifier is coupled to an input of the comparator.
 6. A methodaccording to claim 1, wherein the electrical power fault includeslightning exposure.
 7. A method according to claim 1, wherein theelectrical power fault includes an electrical power surge.
 8. A methodaccording to claim 1, wherein the device comprises either a microelectrical-mechanical system or solid-state relay device.
 9. A methodaccording to claim 1 further comprising protecting the device againstvoltage pulses using the over voltage suppressor.
 10. A method accordingto claim 1 further comprising protecting the device against currentpulses using an over current protector.
 11. A apparatus for protecting adevice against damage resulting from an electrical power fault, thedevice being positioned in a copper loop in a telecommunication network,the apparatus comprising: a sensing resistor for detecting a current inthe copper loop in a double end exposed system; an over current detectorfor detecting and comparing the sensed current with a threshold currentassociated with the device, wherein the over current detector divertsthe current flow from the device if the value of the sensed current isgreater than the value of the threshold current; and an over voltagesuppressor for receiving the diverted current flow, and wherein the overvoltage suppressor limits an electrical power fault voltage that isexposed to the device.
 12. An apparatus according to claim 11, whereinthe over current detector is adapted to generate a signal to trigger theover voltage suppressor.
 13. An apparatus according to claim 11, whereinthe over voltage suppressor comprises a TRIAC.
 14. An apparatusaccording to claim 13, wherein the over current detector comprises anamplifier coupled to a comparator.
 15. An apparatus according to claim14, wherein an output of the amplifier is coupled to an input of thecomparator.
 16. An apparatus according to claim 11, wherein the overvoltage suppressor comprises a zender diode coupled to a pair oftransistors.
 17. An apparatus according to claim 16, wherein the overcurrent detector comprises an PN junction of one of the pair oftransistors.
 18. An apparatus according to claim 11, wherein the overvoltage suppressor is adapted to protect the device against voltagepulses.
 19. A system for protecting a device against damage resultingfrom an electrical power fault in a double end exposed system, whereinthe device is positioned in a copper loop in a telecommunicationnetwork, the system comprising: means for detecting a current in thecopper loop; means for comparing the sensed current with a thresholdcurrent associated with the device; means for diverting the current flowfrom the device to an over voltage suppressor if the value of the sensedcurrent is greater than the value of the threshold current; and meansfor limiting an electrical power fault voltage that is exposed to thedevice using the over voltage suppressor.
 20. A system according toclaim 19, wherein the means for detecting the current comprises an overcurrent detector coupled to a sensing resistor on the subscriber loop.21. A system according to claim 20, wherein the means for comparing thesensed current with the threshold current comprises using the overcurrent detector.
 22. A system according to claim 21, wherein the overcurrent detector is adapted to generate a signal to trigger the overvoltage suppressor.
 23. A system according to claim 20, wherein the overvoltage suppressor comprises a TRIAC.
 24. A system according to claim23, wherein the over current detector comprises an amplifier coupled toa comparator.
 25. A system according to claim 24, wherein an output ofthe amplifier is coupled to an input of the comparator.
 26. A systemaccording to claim 20, wherein the over voltage suppressor comprises azender diode coupled to a pair of transistors.
 27. A system according toclaim 26, wherein the over current detector comprises an PN junction ofone of the pair of transistors.
 28. A system according to claim 19,wherein the device comprises either a micro electrical-mechanical systemor solid-state relay device.
 29. A system for protecting a deviceagainst damage resulting from an electrical power fault in a double endexposed system, wherein the device is positioned in a copper loop in atelecommunication network, the system comprising: at least two sensingresistors for sensing a current in the copper loop, wherein each of thesensing resistors is positioned on the opposite side of the device; atleast two over current detectors for detecting and comparing the sensedcurrent with a threshold current associated with the device and adaptedto divert the current flow from the device if the value of the sensedcurrent is greater than the value of the threshold current, wherein eachof the over current detectors is positioned on the opposite side of thedevice; and at least two over voltage suppressor for limiting anelectrical power fault voltage that is exposed to the device, whereineach of the over voltage suppressor is positioned on the opposite sideof the device.